1. Field of the Invention
The invention relates to a method for determining the oil temperature in an internal combustion engine.
2. Description of the Prior Art
The current temperature of the engine oil is required for certain functions in an electronic control system for internal combustion engines. For example, the exceeding of a threshold value for the oil temperature of the engine can be used to trigger on-board diagnostics. Another known use of the oil temperature is as a criterion for adjusting the idling speed of an internal combustion engine, as at very high oil temperatures a higher idling speed is necessary in order to provide the internal combustion engine with an adequate supply of the then low-viscosity oil. The oil temperature can additionally be used for oil lifetime calculations, enabling the time for an oil change to be optimally determined.
For all these purposes, the known procedure is to measure the oil temperature using an oil temperature sensor and to process the oil temperature sensor signal in the appropriate manner. However, determining the oil temperature by means of the oil temperature sensor is very inaccurate, particularly in the warm-up phase of the oil when the internal combustion engine is not at normal operating temperature.
U.S. Pat. No. 5,002,026 discloses how the oil temperature can be used to adjust the idling in the normal operating range of an internal combustion engine, the oil temperature being determined from other variables in order to obviate the need for an oil temperature sensor. For this purpose, the period of time during which the coolant temperature is equal to or greater than a temperature threshold value is determined. A predefined relationship between this period of time and the oil temperature is determined as a measure for the oil temperature and the idling speed is adjusted accordingly.
Another method for adjusting the idling of an internal combustion engine is known from U.S. Pat. No. 5,623,902 wherein overheating of an internal combustion engine necessitating an increase in the idling speed is detected when an oil temperature equivalent variable determined as a function of the coolant temperature, intake air temperature, engine speed and load of an internal combustion engine exceeds a threshold value.
However, all these methods are unable to provide a precise value for the oil temperature. They are merely designed to detect when the oil temperature exceeds a threshold value.